Apparatus for surveying lateral holes extending from earth bores



April 1, 1958 J. s. M CUNE APPARATUS FOR SURVEYING LATERAL HOLES EXTENDING FROM EARTH BORES 3 Sheets-Sheet 1 Filed Aug. 30 1951 I v I 1 I till I o [H INVENTOR John 5. Mc Cune FIG.I

AT TO R N EY S April 1, 1958 J. s. MOCUNE APPARATUS FOR SURVEYING LATERAL HOLES EXTENDING FROM EARTH BORES 3 Sheets-Sheet 2 Filed Aug. 30 1951 John 8. Mc Cune \\\\A\\ n dllllrrlllllllldfl/lllfrll/lllllllllllll 411111 I; A 4A 1 A A A I; If 1 I I I A T TO R N E YS April 1, 1958 J. 5. MOCUNE APPARATUS FOR SURVEYING LATERAL HOLES EXTENDING FROM EARTH BORES 5 Sheets-Sheet 5 Filed Aug. 30, 1951 FlG.-5

INVENTOR. John 8. Mc Cune J 11,115 wa m g nited t mil APPARATUS FOR SURVEYING LATERAL HOLES EXTENDlNG FROM EARTH BORES John S. McCune, Denver, Colo., assignor to Eastman Oil Well Survey Company, Denver, (3010., a corporation of Delaware Application August 30, 1951, Serial No. 244,384

14 Claims. (Cl. 33-205) drill off from the main bore one or more laterally directed holes to increase the oil production from the reservoir to which the main well bore has been drilled or for other purposes such as, for example, exploration.

Generally there are several of these drain holes and it is desirable that they be drilled off from the main bore at vertically spaced points, and preferably also that they extend from the main bore in different directions and with the desired spacing. These drain holes have a very high angle with respect to the main bore and in this respect difi'er from a mere deflected bore. When a drain hole is started to be drilled, it of course is easy to ascertain at what depth it is being drilled off from the main bore and its initial direction. Thereafter, the drain hole may have its direction changed from that contemplated, due to the use of flexible shafting employed in performing the drilling. if it is not known exactly where each drain hole is drilled, then during the drilling thereof the proper spacing cannot be accomplished with any certainty. To know this position of each drain hole, surveying thereof must be done, but such is not possible with presently used equipment. Therefore, the principal object of my invention is to provide apparatus for surveying holes which are drilled to extend laterally at a high angle from a main earth bore extending downwardly into the earths formations so that the exact position, inclination and direction of inclination, of any portion of the hole with relation to the main bore will be known.

Another object of my invention is to produce apparatus which will permit a well survey instrument to be so attached to a stem extendable into a main bore that it will be directed into the open end of a lateral drain hole and can thereafter be positioned at various points throughout the length of the drain hole in order that recordeddata can be obtained relative to the position of the hole at such points.

A further object is to produce improved means for connecting a well survey instrument to a stem so that the axis of the survey instrument can be caused to be at an angle to the axis of a main well bore with its forward end directed toward one side wall of said main bore and thus permit, upon lowering of the stem, the survey instrument to easily enter the open end of a lateral drain in the side wall of said main bore. Yet a further object is to so construct the connecting means between a survey instrument and stem that it will embody such flexibility that the survey instrument, after being caused to enter the drain hole, can be moved to different points along the path of said drain hole so that recorded data can be obtained at such points to determine their position with respect to the main well bore. said connecting means also being of such construction as to insure tes Patent bore and which will also have such flexure that the instrument can be moved along the path of the drain hole by a lowering movement of the stem after the instrument has been caused to enter the said lateral drain hole.

Other objects of my invention will become apparent from the following description taken in connection with the accompanying drawings in which several different forms of apparatus each embodying the invention, are illustrated for carrying out my new method.

In the drawings:

Figure 1 is a view showing one form of apparatus for carrying out my new technique of surveying drain holes and including connecting structure for facilitating the entry of the survey instrument into the drain hole and moving it therein to any position where it is desired to obtain data pertaining to the positions of the drain hole;

Figure 2 is an enlarged sectional view showing a portion of a survey instrument that can be employed in making a survey of a drain hole;

Figure 3 is a view showing another form of connecting apparatus which can be employed between the survey instrument and the drill pipe for facilitating the entry of the survey instrument into the drain hole and moving it therein to any desired position;

Figure 4 is a View showing still another form of apparatus which can be employed to carry out my new technique of drain hole surveying;

Figure 5 is a view showing still another connecting structure of the knuckle joint type whereby the survey instrument can be directed into the open end of the drain hole and moved therein to perform surveying;

Figure 6 is a view similar to Figure 5, but showing the knuckle joint tripped so as .to place the survey instrument at an angle to the axis of the main bore and direct it toward the drain hole opening; and

Figure 7 is a sectional view of another type of knuckle joint which can be used, said joint being normally held deflected by a leaf spring embodied therein.

Referring to the drawings in detail and first to Figure 1, there is disclosed a main bore B of an oil well which has been drilled into the oil producing strata for recovering oil therefrom. In order to increase the oil production from this reservoir to which the main bore has been drilled, lateral drain holes, such as D, have been drilled off from the main hole at a high angle by suitable flexible shaft structure. These drain holes will generally be drilled off from various spaced distances from the main bore and may or may not be in different directions. It is desirable, as already pointed out, to know the exact location of these drain holes, andparticularly the direction in which they extend so it will be known whether the reservoir is being properly and efficiently drained. a r

In surveying these drain holes to obtain the information from which it can be ascertained where the drain holes are positioned, I employ asurvey instrument S. This survey instrument may be of any'suitable type for obtaining the desired data. It could be of the multiple shot type which is capable of obtaining a series of: recorded data by photographic means, said data being the inclination of the axis of a hole to the vertical and the direction in which said hole extends. It could also be a so-called single shot instrument which records recorded data as to the inclination only of the hole, such an instrument generally being called a drift indicator.

The instrument S will have a suitable rounded nose end it) thereon so that its entry into the opening of the lateral drain hole will be facilitated. At the upper end of this instrument there is provided an attaching joint 11 for attaching the instrument tothe lower end of a long flat leaf spring 12. At the upper end of this leaf spring, which will be of considerable length, there is a connector 13 whereby the spring is attached to the lower end of a drill pipe P, the connection being accomplished in a suitable manner such as shown by internal threads in the connector 13 which cooperate with external threads on the end section of the drill pipe. The connection between the survey instrument and the drill pipe is such that relative rotary movement cannot occur. This end section of the drill pipe may be a flexible rod if it is desired to have the leaf spring of less length than the length of the hole to be surveyed. If the leaf spring is to be the sole flexible member between the survey instrument and the normal drill pipe, then it will be slightly larger than the length of the drain hole. The flat leaf spring 12 will have a normal bowed condition as is indicated in Figure 1. With this bowed condition the instrument S will be positioned so that its axis will be at an angle to the axis of the main bore B as the instrument 8 is run into the main bore. Because of this angular positioning of the survey instrument the nose end 16 thereof will be directed toward one side of the man here and will be pushed along said side as the instrument is lowered into the main bore.

When the drain holes D are drilled it is known at what depth the open end of each is from the surface. This will be known because of the length of drill pipe in the bore when the drilling of the drain hole was started. With this knowledge as'to the depth of the entrance to the drain hole, it will be seen that the drill pipe can be lowered with the instrument S connected to the lower end thereof by the leaf springand when the proper depth is reached it will be known that the instrument is at the entrance of the drain hole D. By then turning the drill pipe around in the bore, the nose of the instrument will be moved around the inner wall of the main bore and be pressed into the open end of the drain bore under the action of the normally bowed leaf spring. After the nose enters the drain hole, the instrument S can be moved into the drain hole by lowering the drill pipe. Due to the flexibility of the leaf spring, it will follow the curvature of the drain hole in an easy manner. If the leaf spring is shorter than the drain hole and a section of flexible rod is used above the leaf spring, the rod will then follow the leaf spring into the drain hole as the instrument is pushed to the end thereof.

If, for example, a multiple shot survey instrument is used in making the survey, the instrument will be stopped at different points in the drain hole and recorded date obtained onthe film. In order that it will be readily understood how such amultiple shot survey instrument operates, there is disclosed in Figure 2 a sectional view of part of the structure of such an instrument. The instrument will have a barrel 14 formed from various sections screw connected together. This barrel is positioned in a non-magnetic housing H carrying the nose 10. In the lower end of the barrel 14 will be the angle b unit A. Above this angle unit will be the camera unit C'for photographing and recording the indications of the angle unit and this camera unit will be controlled by a time unit T, only partially disclosed.

The disclosed angle unit A is what is called a 18-90 combination unit. An angle unit such as this type will be necessary'in properly surveying a drain hole because these drain holes are drilled off from the main bore of the well at a high angle and then continued until they may extend in substantially "a horizontal direction, or even above the point of take off from the main bore. Since the angle unit disclosed is of well known construction, it will only be briefly described. It has two sections A and A". In the A section is the 90 apparatus having a compass 15 mounted on a pivot pin 16. This compass will carry a card assembly 17. The pivot pin will be mounted on a rocker 18 which is mounted by pivots 19 to the rocker yoke 29. Thus, the compass is capable of swinging through an 180 degree arc, thus giving readings of 90 on each side of vertical. Above the compass is graduated drift are 21 for indicating the angle and associated therewith is the cross hair 21'. The compass is covered by a concavo-convex glass top 22 having concentric circles to indicate degrees. The rocker yoke of the compass, upon which the compass is mounted, is pivoted on a vertical axis by a spindle 23 suitably journaled in a support structure 24. There is also shown a sylphon 25 which, with the chamber in which the compass is mounted, is all filled with a suitable liquid for lubricating the spindle and also acting as dampener and a shock absorber. The sylphon allows for expansion and contraction of the liquid.

The A" section of the angle unit includes a plumb bob '26 having a cross hair ring 27 thereon and being suitably mounted by a gimble structure 28 for universal swinging. This section shows inclinations up to 18 degrees, which range is not accurate on the 90 section just described. The position of the plumb bob over the concentric circles on the glass 22 indicates the angle of inclination.

The camera unit C above the compass is provided with lights 29 connected to a battery not shown. Above the lights, which are mounted in a partition, is the film 36 extending over suitable reels. This film passes across the upper end of the lens tube 31 in the partition, having a suitable lens therein. The film will be moved by suitable clock mechanism in the time unit T, the Geneva wheel 32 thereof only being shown. It is by means of this Geneva wheel that the film will be moved periodically. There is also shown a switch 32' which is part of the camera unit. This switch controls the illumination of the lights 29 and in turn is controlled by the clock mechanism.

With this description of the survey instrument, it is believed to be obvious that after a setting of the time mechanism at the top of the main bore and a moving of the 'survey instrument into the main bore and then in the drain hole, the compass of the angle unit will be periodically photographed. The camera will operate at timed intervals and when the survey instrument is stopped for proper periods at various positions along the path of the drain hole, the clock mechanism will cause a photograph to be made. After this is accomplished the film will be moved by the time mechanism and the Geneva wheeland set for the next exposure, which will be taken when the instrument has'been moved to another position and then held there until the exposure takes place under the control of the time unit. If the drain h'ole should go above the horizontal plane of its inlet, the survey instrument can be reversed on the end of the leaf spring, if this part of the drain hole is to be surveyed.

In Figure 3 there is shown another connecting means that can be employed'between "the survey instrument S and aiflexible end section P'On the end of the drill pipe.

This'connecting'means comprises aituhe 33 made of flexible material. curvature. The upper end is arranged to be threaded to the lower end of the flexible end section 1 by a connecting collar 34 and the lower end attached to the upper end of the housing of the survey instrument by a connecting collar-35. The flexible tube, when in its normal curved condition (shown by dashed lines), will cause the axis of the survey instrument to be at an angle to the axis of the main bore'll with its nose end .19 directed.

toward the wall of the bore so that when the instrument The tube is constructed to have a normal.

ascends 55 is at the depth of the open end of the drain hole the instrument can readily enter the drain hole.

In order to facilitate the lowering of the survey instrument down the main bore and prevent it from being directed toward a side wall of the bore during said lowering, there is associated with the flexible tube 33 a straight rod 36 inserted therein, as shown in Figure 3. This rod will be placed in the tube before the instrument is lowered into the well and thus the tube will be held straight and the instrument will go into the main well bore in an easy manner. When the instrument is at a depth opposite the drain hole which is to be surveyed, an overshot can be lowered on a line through the drill pipe bore and be caused to engage a spear head 37 on the top of the rod 36. The rod can then be pulled out of the tube by pulling upwardly on the line. When the rod is removed, the tube will then tend to take its set curvature as shown in dotted lines in Figure 3. This will cause the instrument S to have such an angular position in the well bore that its end can readily enter the drain hole upon lowering the drill pipe. The tube 33 need only be of a relatively short length when the flexible end section P is employed. When the instrument has been caused to enter the drain hole and the entire flexible tube 33 is moved into the drain hole, the flexible section P will follow into the drain hole and flex sufliciently to permit the instrument to be continued to be moved into various positions in the drain hole where the survey instrument will be operated to obtain the desired recorded data. It if should not be desired to use the flexible section P, then the tube 33 will be made long enough so it can extend to the end of the drain hole.

The connecting flexible structure between the instrument and the drill pipe shown in Figure 3 is such that circulation of fluid will be permitted. To accomplish this the connecting collar 35 will be provided with a plurality of outlet holes 35'. If the flexible section P is used, it will be tubular so that fluid can flow down the drill pipe into the tube 33 and out the holes 35'. Circulation of fluid may be found desirable to aid in opening a drain hole or to free a stuck instrument or for other purposes.

Still another form of connecting means which can be employed between the survey instrument S and the drill pipe is shown in Figure 4. This connecting means disclosed comprises a flexible shafting made up of a plurality of short sections 38. The sections will be joined together by suitable joints 39, as for example, of the type in which circular lugs are carried by one end of a section 38 for fitting into circular slots in the end of an adjacent section 38. The inter-engaging projections and slots will be so constructed that the shaft will have the desired flexibility in any direction, but there cannot be any relative rotation between the pipe and the survey instrument S. Above the flexible shafting formed by the sections 38 there will be an adapter 40 and this adapter will be connected to the drill pipe. In order that the survey instrument and the short sections of the flexible shaft may be properly deflected into the drain hole D, there is provided a deflector housing 41. This housing is a tube 42 having a reduced upper end opening 43 in surrounding relation with the drill pipe DP. Near the lower end of the tube 42 is a window 44 and associated with this window is a deflector 45 which has an angular surface so that the lower end of the instrument can engage the deflector as it is lowered and thereby be directed into the open end of the drain hole D. The tube 42 of the deflector housing will be of a length to permit the flexible shafting and survey instrument to be withdrawn into the tube. The flexible shafting will be of a length suflicient to move the instrument to the end of the drain hole.

The adapter 44] is provided with a key 40 which is arranged to be received in the slot 43 of the reduced upper end of the deflector housing. A shear pin 40" will also be provided to connect the adapter to the upper end of the tube when the key is in the slot. With this arrangement, the deflector housing can be attached to the adapter at the top of the main bore and the assembly lowered into the main bore. When the window in the deflector housing is at the proper depth the housing can be oriented in a well known manner by rotating the drill pipe and thus placing the window opposite the open end of the drain hole to be surveyed. Now, by lowering the drill pipe, the shear pin will be severed and the instrument guided into the drain hole to begin the surveying. If the drain hole is at the bottom of the main bore, the deflecting housing can set on the bottom of the main bore. If the open end is above the bottom of the main bore, it can be supported by a tail pipe 41 of a proper length, all as shown in Figure 4. When the surveying is completed,the flexible shafting will be withdrawn into the deflector housing and if another hole at the same depth is to be surveyed, the key and slot arrangernent will permit the housing to be properly oriented to the desired position.

Circulation of fluid through the flexible shafting can be accomplished by making the sections tubular and placing inside thereof throughout the entire length of the shafting a rubber hose so there will be no leaking outlet holes in the connector 38' between the shafting and survey instrument, all as shown in Figure 4.

Still another form of connection which can be used between the survey instrument and a flexible pipe section P at the lower end of the drill pipe or stem is a unidirectional knuckle joint shown in- Figures 5 and 6 and generally indicated by the letter K. The knuckle joint, as shown, has a lower member 46 provided with a sphericallike socket 47. Cooperating with the member 46 is a second member 48 having a ball-like end 49 thereon for reception in the spherical socket. The ball is provided with recesses 50 into which lugs 51 project, thereby holding the ball and socket together and preventing relative rotation of the members. The upper end of the member 46' above the socket is provided with an angular end 52 and the passageway between this end and the socket has a flared part 53, thus permitting the member 46 to be swung in one direction only so that its axis can be at an angle to the axis of the member 48 which carries the ball. Mounted for sliding movement on the member 48 is a collar 54 and acting on this collar is a strong coil spring 55 interposed between the upper end of the collar and a nut 56 screwed onto the upper end of the member 48. The nut 56 is held in adjusted position by a lock nut 57. The upper member 48 of the knuckle joint has a window 58 adjacent the collar 54 and pivotally mounted in this window is a latch 59, the tail end of which is arranged to project into a bore extending downwardly through the upper member 48 of the knuckle joint and arranged to communicate with the bore of the pipe P to which the upper member 48 of the knuckle joint will be attached by the usual threaded joint.

The latch 59 can be set to normally hold the collar 54 in its inoperative position, as shown in Figure 5, and when in this position the. spring 55 will be compressed and the collar cannot act downwardly on the upper angular end of the member 46 of the knuckle joint. When the collar 54 is latched upwardly, as shown in Figure 5, the tail end of the latch will project into the bore 60. When the knuckle joint is in this condition, the two parts 46 and 48 0f the knuckle joint-can hang in axial alignment. Thus, with the instrument S attached to the pipe P by this knuckle joint, it can be easily lowered into the .well bore toa point adjacent the openend of a drain hole. There will be no danger of the nose end of the instrument catching on the side wall of:

the bore during the lowering of the instrument.

After the instrument has reached a point opposite the open end of a drain hole, the knuckle joint can be operated so it will cause the instrument S to have its axis angularly positioned in the bore with its nose end directed toward a side wall of the bore. To accomplish .joint. This tripping rod 61 is shown in Figure 6 positioned in the bore 60 where it has already engaged the tail end of the latch and operated this latch so as to release the collar 54. When the collar is released, the compressed spring 55 will act thereon and force it downwardly so it will engage the upper end of the member 46 of the knuckle joint. Since this upper end is angularly related to the axis of the member it will cause a swinging of the member 46 relative to the member 48 which is permitted by the ball and socket connection. The amount of swinging will be predetermined by the angularity of the top end of the member 46 above the spherical socket. With this angular relationship between the members 48 and 46 being brought about by releasing the latch 59, the instrument S can be readily inserted into the open end of a drain hole when the drill pipe is properly oriented and lowered.

To provide for circulation, the bore 6!) can extend to the end of member 43 and communicate with abore 46" in the member 46 with branch bores leading to the exterior of said member 46. If a flexible pipe section P is not desired to be used, then it can be replaced by flexible shafting like that shown in Figure 4.

In Figure 7 there is shown a more simplified type of knuckle joint which is yieldably biased so that the members thereof are out of alignment. As shown, the knuckle joint has a lower tubular member 52' and an upper tubular member 63. The lower tubular member has a spherical upper end 64 which is received in a spherical socket 65 in the lower end of the upper tubular member. A nut es holds the spherical end 64 in the socket. A strong curved leaf spring 67 is mounted in the bores of the tubular members, as shown. One end of this spring, such as the upper end 68, will be attached to a tubular member, the other end being free.

in usin this knuckle joint, the lower tubular member 62 will be connected to the survey instrument S and the upper member either to a flexible section or flexible shafts such as, for example, that shown-in Figure 4. The survey instrument will then have its axis so positioned as to be at an angle to the axis of the main bore, all because of the action of the spring 67 on the lower member of the knuckle joint. Thus, the survey instrument can be easily moved into the open .end of a drain :hole when the lower end of the survey instrument is lowered to a point opposite said open end. There can be circulation through the knuckle, due to the tubular members.

From the foregoing description of the various structures embodying my invention and employed for connecting a survey instrument to a drill pipe, it will be seen that eflicient surveying of lateral drain holes of wells can be accomplished. The well surveying instrument can be easily inserted into the open end of a drain hole drilled oil from the main bore at a high angle and thereafter moved to different positions throughout the length of the drain hole to obtain recorded data relative to the position of the drain hole with respect to the main bore. This information may be the direction in which the drain hole extends or the angle of the drain hole withrespect to the main bore, or both such data, depending upon the type of instrument which will be employedin making the survey. The survey instrument will be set ioroperation at the top of the well bore and when the instrument is allowed to remain stationary the necessary period, the recorded data will be obtained. If it shouldbe desired to circulate fluid diuing the surveyin operatiom-such can he done, as for example, by using the 'fiexibleshafting shown in Figure 4, the flexible-tube shown in Figure 3 or the knuckle joints. Since the survey instrument, by all connections shown; is connected to the drill pipe so that there is no relative rotation between the two, an oriented survey can be made in the drain hole from the surface. If an oriented survey should not be desired or his not necessary to turn the instrument so as to direct it toward 'the'open end of the drain hole, the connection could be such that relative rotation was permitted between the instrument and drill pipe. For example, the flexible shafting of Figure 4 could permit relative rotation as the directing of the instrnmentinto the drain hole is accomplished by the deflecting surface arranged to be rotated by the drill pipedirectly. i

Being aware of the possibility of modifications in the particular structure shown for carrying out my novel method of surveying lateral drain holes of well bores, all without departing from the fundamental principles of my invention, I desire'it to be understood that the scope of my invention is'not to be limited in any manner except in accordance with the appended claims.

What is claimed is:

1. In apparatus for locating and surveying a drilled drain hole of 'an oil well which drain hole extends laterally at a high angle from a drilled main bore and having an openend in the side wall of said main bore, said apparatus comprising a survey instrument capable of obtaining when operated recordeddata as to the position of any portion of the drain hole in the earth, an elongated casing for the instrument, means for connecting the upper end of the survey instrument casing'toa stem extendable into the main bore from the earths surface, said connecting means comprising an elongated freely flexible structure conformable. at will and at all times to the unknown contour of the previously drilled drain hole whereby the instrument maybe moved ahead of it into the drain hole a substantial and selected distance upon lowering of the stem in the main bore, and means for placing the axis of the instrument at an angle to the axis of the main bore so that the entry of the lower end of the instrument easing into the open end of the drain hole will be facilitated. i

2. The survey lapparatus called for by claim 1 wherein the last named means constitutes means embodied in the connecting means for yieldably biasingthe axis of the instrument to a position where it will be at an angle to the axis of the main bore.

3. The survey apparatus called for by claim 1 wherein the last named means constitutes a hinged joint embodied in the connecting means, and spring means for biasing the joint so that the axis of the instrument will be at an angle to the axis of the main bore and stem.

4. The survey apparatus called for claim 1 wherein the last two named means constitute a connecting means made of a flexible material having such normal curved condition that the axis of the instrument will be placed in a position so that the lower end thereof will be directed toward the open end of the drain hole.

5. The survey apparatus called for by claim 1 wherein the last two named meanscons'titute at least in part a leaf spring having a bowed condition.

6. The survey apparatus called for by claim 1 wherein the last two named means constitute a tubular member made of rn'ateria'l permitting flexing thereof so that it can enter and follow the drain hole and said tubular member having a normal bowed condition.

7. The survey apparatus called for by claim 6 together with a removable straight rigid rod positionable in the tubular member for maintaining said tubular member straight during the movement thereof into the main bore. p

8. The survey apparatus called for by claim 1 wherein the last named means constitutes a hinged joint embodied in the connecting-means, means including spring means for normally causing the members of the hinged joint to have an angular relation of less than 90 degrees, and means including releasable latch means for holding said members in aligned condition.

9. The survey apparatus called for by claim 8 together with means for releasing the latch means at will.

10. The survey apparatus called for by claim 1 wherein the last named means constitutes a deflecting member positionable in the main bore with the stem and the flexible connecting structure.

11. The survey apparatus called for by claim 10 wherein there is embodied means for connecting the deflecting member for rotation with the stem to thereby permit the said deflecting member to be oriented with respect to the drain hole opening.

12. The survey apparatus called for by claim 1 where in the flexible structure constitutes a flexible shaft made from short members, and connecting joints embodying projections on the end of one member and receiving slots on the adjacent end of the next member.

13. The survey apparatus called for by claim 1 wherein the flexible connecting structure is provided with conduit means having outlets just above the instrument so as to permit circulation of fluid while the survey instrument is in either the main bore or in the drain hole.

14. In apparatus for locating and surveying a drilled drain hole which extends laterally from a drilled main earth bore with an open end in the side wall of said earth bore, said apparatus comprising a survey instrument capable of obtaining when operated recorded data as to the position of any portion of the said drain hole in the earth, an elongated casing for the instrument, and means for connecting the upper end of the instrument casing to a stem extendable into the main earth bore, means for positioning the longitudinal axis of the casing of the instrument at an angle to the axis of the main earth bore with its lower end in a position to enter into the open end of a drain hole when the stem is lowered, said connecting means including means preventing relative rotation between said casing and stem and comprising an elongated freely flexible structure conformable at will and at all times to the unknown contour of the previously drilled drain hole whereby the instrument may be moved ahead of it into the drain hole a substantial and selected distance upon lowering of the stem in the main bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,820 Lee Nov. 8, 1932 2,016,042 Lewis Oct. 1, 1935 2,114,476 Ragland Apr. 19, 1938 2,118,650 Lee May 24, 1938 2,179,832 Smith Nov. 14, 1939 2,187,028 Hendrickson Jan. 16, 1940 2,327,658 Miller Aug. 24, 1943 2,364,908 Miller Dec. 12, 1944 2,373,976 Ranney Apr. 17, 1945 2,508,899 Trotter et al. May 23, 1950 2,634,097 Zublin Apr. 7, 1953 OTHER REFERENCES PubL: Haddock Deep Borehole Surveys and Problems, pages 162l65, McGraw-Hill C0., 1931. 

